Method of making terminal construction for electrical circuit device

ABSTRACT

An electrical circuit device having a substrate including circuit components on at least one side thereof and a plurality of through openings in the substrate. Terminal leads are positioned in the openings each with a deformation intermediate the ends of the leads and spaced internally of the opening from a soldered area at the juncture of the exposed portion of the leads and the termination edge of the substrate. Two methods of assembly of leads to the substrate are also disclosed.

This is a division, of application Ser. No. 609,780 filed Sept. 2, 1975,now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to electrical circuit devices, and particularly toa method for anchoring and connecting lead wires to such devices.

In recent years there has been an increase in the usage of circuitdevices comprising substrates of ceramic material such as alumina,steatite or other materials, wherein at least one surface of thesubstrate includes a deposited thick or thin film electrical circuit.The devices are generally modular and may include, in addition toresistive and capacitive elements, the addition of discrete componentsto provide hybrid circuits. It will be obvious that means forterminating the electrical circuitry is of equal importance to thecircuitry itself in order to provide an acceptable unit. Circuitsfundamentally depend upon the integrity of electrical continuity throughthe termination and lead wires required for connection to printedcircuit boards or other circuit components. Various developments havebrought forth techniques for terminating, each of which has beendesigned to provide the necessary electrical continuity with the circuitand strength to achieve proper pull force at the connection between thelead wire and the termination of the circuitry. In addition, theconnection must be solid and stable so as to minimize electrical "noise"problems.

Terminating techniques and provisions of terminal leads have beenillustrated in various patents most of which have been reviewed in U.S.Pat. No. 3,873,890 issued to Beckman et al and assigned to the sameassignee as the present invention.

The device and method disclosed herein, although having applicationelsewhere, are principally related to so-called SIP (single in-linepackaging) devices which are generally arranged to be supported in aposition substantially normal to the plane of a printed circuit board orother mounting surface. Such devices may contain as many as seven oreight spaced apart lead wires closely positioned relative to oneanother.

The above-mentioned U.S. Pat. No. 3,873,890 teaches the insertion andretention of lead wires into a side of a ceramic substrate having anelongated groove divided into juxtaposed alternately distended andconstricted portions, the constricted portions being adapted to receivethe end portion of relatively flat lead wires. The constricted portionis metallized prior to receiving the lead wires and the lead wires arethen inserted and soldered in place. The construction taught by Brady inhis U.S. Pat. No. 3,346,774 disclosed a device which utilizes asubstrate having lead wires anchored in cavities are of a sizeinsufficient to freely receive the lead wires. The lead wires of Bradyare forced into the cavity of the substrate to fixedly secure the leadwire directly to the substrate. The lead wire is further soldered inplace to previously deposited metallized areas which areas include theentrance to the said cavities.

The Ragan U.S. Pat. No. 3,277,232 teaches a means of terminating anelectrical circuit device with openings formed to traverse a substratefrom end to end, and which substrate is arranged to receive oppositelydisposed lead wires. Each lead wire has an end upset or bent to providean obstruction externally of the substrate, which bent or upset headedportion is secured to the substrate by means of solder adhering to ametallized area, which is also connected to an electrical circuitdisposed on the substrate.

Except for the Beckman et al. patent, most previously developed deviceswere designed to receive individual leads, whereas Beckman et al. andthe device of the present invention are arranged to take advantage of"lead frame" construction, wherein a plurality of integrally formedleads project laterally from a common carrier portion of the frame. Thistype of construction leads itself to use in automated assembly,insertion, soldering and trimming apparatus. Previous devices suggestindividual lead insertion techniques. Further consideration of thepresent disclosure, however, will reveal that although the best mode isconsidered to be in the form of so-called lead frame assembly, theinvention may also utilize techniques of individual insertion of leadwires.

SUMMARY OF THE INVENTION

The present invention contemplates a method and means for anchoring andconnecting leads to an electrical circuit device, wherein theconfiguration of the circuit is deposited on at least one surface of aninsulating substrate. The substrate may be made of ceramic material,such as alumina or steatite and is pressed or otherwise formed toinclude a plurality of spaced apart, through openings traversing thesubstrate from one side to side. It is usual to provide the substrate asa rectangular, box-like object defining four sidewalls, which sidewallsare intercepted by the plurality of through openings. However, the exactconfiguration should not be considered so limited, as it will beapparent that other shapes may embody the concept without departing fromthe basic invention as will hereinafter be described.

In each of the parallel, spaced apart openings there is seated aterminal lead which has an external portion adapted for connection to aprinted circuit board, or other means for connecting the electricalcircuit device with another circuit element.

In the preferred embodiment, the inner portion disposed internally of arespective opening defines a crimped or corrugated, or otherwisedeformed portion which is of such dimension as to be in intimate andrelatively stable contact with the internal wall surface for itsopening. The respective openings are preferably disposed in a planeparallel with a surface supporting the electrical circuitry. Apreprinted edge termination area is deposited to traverse the opening,and preferably slightly inwardly thereof, and overlapping the surfacecontaining the electrical circuitry to make contact with thick or thinfilm laid down upon that surface. The unit is solder dipped, with thesolder gripping the lead at the juncture of the inner and outer portionsof the lead and adhering to the preprinted edge termination area. Thepreprinted area is preferably of a known silver base which readily joinswith the solder and the substrate material. The electrical circuitry maybe applied to one side or to both sides of the substrate as required.

One interesting aspect of the present invention relates to the fact thatshould an ultimate user so desire, the usual conformal insulatingcoating may be omitted from the edge opposite the edge from which theleads extend. Thus, the exposed edge may provide means, if so desiredand the circumstances permit, for testing circuitry with probes adaptedto enter the openings and contact ends of the leads exposed in theopenings. Also, it is conceivable that "cross over" connections may bemade between the leads by preprinting and soldering an edge terminationextending between adjacent openings and the distal ends of the internalportions of the leads disposed in the openings. In the latter case itmay be desired to cover the solder area with a conformal insulatingcoating to minimize the possibility of short circuiting the device withanother device or another printed circuit board positioned adjacent tothe device.

The invention is further exemplified in the preferred method of assemblywherein the leads are deformed externally and are withdrawn afterdeformation to be positioned within the openings in the substrate, aswell as presenting variations of lead configurations. Obviously, afterconsidering these variations, it will become apparent that additionalmodifications may be made without departing from the scope of theinvention.

One of the preferred methods utilizes an indefinite length of lead framehaving a carrier strip portion from which there extends a plurality ofspaced apart elongated lead members. The lead frame is stamped from flatmetal stock and preferably includes a plurality of spaced apart guideopenings for registering and indexing the stock during the stage ofinsertion, deforming and inserting steps as will hereinafter bedescribed. For the purpose of this summary, however, the substratecontaining the circuit components and appropriate edge terminationareas, is positioned on the lead frame with the elongated, flat leadmember being disposed within the openings and extending outwardlythrough the other end of the respective openings. The extending leadportions, with the substrate inserted thereon, are next crimped,corrugated or otherwise deformed preferably at the distal end portionthereof. The substrate and the lead assembly are then moved relative toone another, with the substrate resting against a stationary stop toprovide the desired positioning of the leads in the opening. At thisstage, the leads and the substrate will be held together since thedeformed portion will act to provide intimate contact with the innersurface of the respective openings. The next stage is the application ofsolder, wherein the entire unit may be dipped in solder to coat theleads, the exposed edge termination areas and also to provide a means ofjoining the leads to the substrate. The unit is then encapsulated withan insulating conformal coating, which may be of a material that alsoencloses the exposed end of each opening, if so desired. The final stageinvolves the cutting off the carrier strip. Depending upon the equipmentand other factors, the soldering and coating stages may be in reverseorder.

Another embodiment discloses a substrate having a plurality of spacedthrough openings through which lead portions of a lead frame extend andare then coined at their distal end portions to provide an abutment forintersection with the shoulder of the opening.

Among the several objects of the present invention, is the provision ofan electrical circuit device having lead wire terminations with aportion extending into a respective transverse opening of a substrateand with the distal end being deformed after insertion to resistwithdrawal of the lead wire prior to and after solder is applied to thejuncture of the lead and substrate.

The foregoing and other objects and advantages will appear in thefollowing drawings which form a part hereof and which show by way ofillustration a preferred embodiment of the invention. Such embodimentdoes not necessarily represent the whole scope of the invention, andreference is made to the claims herein for interpreting the breadth ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a substrate suitable for use in thepractice of the present invention;

FIG. 2 is a perspective view of the substrate of FIG. 1 after printingof the edge termination configuration;

FIG. 3 is a perspective view, including the edge termination and atypical resistive network circuit deposition on the upper surface of thesubstrate of FIGS. 1 and 2;

FIG. 4 is a top plan view of a lead frame assembly illustrating sixstages in the process of manufacturing electrical circuit devices of thepresent invention;

FIG. 5 is a top plan view of a lead frame strip illustrating anotherembodiment of the substrate and leads typifying another embodiment ofthe present invention;

FIG. 6 is a cross-sectional view of the device on the present inventiontaken along the lines 6--6 in Stage 6 of FIG. 4; and

FIG. 7 is a perspective view of the finished product with conformalcoating applied and identification printed thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The substrate manufacture and use is best described with reference toFIGS. 1-3, inclusive. An insulating substrate 10 is pressed, orotherwise formed, from a ceramic material such as alumina or steatite toprovide opposed upper and lower planar surfaces 11. Depending from, andangularly relative to, the planar surfaces 11 is a continuous sidesurface indicated generally by the reference character 12 definingopposed parallel surfaces 13 and 14.

Either one or both of the surfaces 11 may contain the electricalcircuitry which may be in the form of a network of resistors, acombination of resistors and capacitors and semiconductor chips, orchips of capacitors or the like. The circuit configuration is made inaccordance with known techniques and does not form the particular partof the present invention.

The opposed sidewall surfaces 13 and 14 include a plurality of spacedapart openings 15 traversing the substrate 11 from sidewall 13 tosidewall 14 (see also FIG. 6). As shown, surface 14 also defines aslight countersunk portion 16 which provides ready access of leads, aswill hereinafter be described. For the purpose of spacing the sidewall14 of the substrate 10 from a circuit board or other means of mounting,the substrate 10 is provided with a pair of forwardly projectingstand-offs 17 and 18.

With reference to FIG. 2, the substrate 10 is provided with edgetermination areas 20. The areas 20 are printed with a conductingmaterial such as silver paste, extending across the face of the surface14 and preferably a bit inwardly of the openings 15, and overlapping thesurface 11 as shown at 21. This overlapping area 21 connects theelectrical circuitry to the edge of the substrate 10, as will later beexplained. The material of the termination areas 20 (in this case silverpaste) is well known and is compatible with solder for connecting theleads as will hereinafter be described. After application, the silverpaste edge termination 20 is fired on the substrate in the usualfashion.

A typical resistive network is shown in the view of FIG. 3, and may beof a thick or thin film material, such as the well known cermet resistormaterials, one of which is described in the Brandt et al U.S. Pat. No.3,639,274, assigned to the same assignee as the present invention. Theparticular composition does not form a part of the present invention.

The resistive areas are denoted by the reference character 23, and inthe case of cermet material, are screen printed or otherwise depositedto extend over the overlapping portion 21 of the edge termination 20.Without going into the details of the circuitry, which is unimportant tothe present invention, a conductive strip 24 of cermet material is laiddown before the resistive layers 23 in known fashion. This material isalso of a glassy matrix including a highly conductive metallic materialintermixed herewith. The layers may be fired individually or co-fired asdesired.

The present embodiment illustrates a single in-line package (SIP) whichincludes, as shown in FIG. 7, an eight leaded construction. FIG. 4illustrates, in six stages, the preferred method of assembly of leads tothe substrate, in accordance with the present invention. A continuouslead frame, indicated generally by the reference numeral 30, is stampedor otherwise formed from a conducting metallic material suitable for usein termination leads. The portion identified as a carrier strip 31preferably includes longitudinally spaced apertures 32 which are usedfor guiding, registering, and conveying purposes. As shown in Stage 4 ofFIG. 4, the apertures 32 may receive index and support the ends 33 forpurposes to be later described. In general, suffice it to say that theapertures 31 may be received by conventional sprocket teeth for movementof the frame 30 in the direction of the arrow, and also for registrationof the lead frame as necessary in the various stages. Integral with andprojecting laterally from the carrier strip 31 is a plurality of spacedapart lead members 35 arranged to be received in the openings 15 of thesubstrate 10. It will be apparent that the countersunk portion 16 of theopening 15 will assist in the reception of the leads 35 as the leadframe 30 is being moved during the several procedural stages.

It is to be noted, that although the various stages are indicated astaking place immediately in sequence, with the substrates 10 adjacent toone another, an indefinite number of substrates may be used in each ofthe stages along the lead frame 30 in accordance with known assemblytechniques.

With reference to FIG. 4, Stage 1, it will be observed that therelatively flat termination lead members 35 of the lead frame 30 areinserted into the respective openings 15 of the substrate 10. Asindicated at Stage 2, the substrate 10 and the carrier strip 31 aredrawn toward one another to expose the distal end portion of the leadmember 35. This permits freedom of access to the exposed portions of theleads for purpose of seating the leads in a "bumping" or forming tool(not shown). The die members of the tool are designed to provide adeformation of the extremities as shown in Stage 3 of FIG. 4 and FIG. 6.Here, the deformation takes the form of undulations or corrugations 36which serve to extend the thickness of the lead members 35 in "spring"fashion. As shown in Stage 4 of FIG. 4, the substrate and the carrierstrip 31 are drawn away from one another in the direction of the arrow.A stationary stop member 37 is provided to position the substraterelative to the ends of the leads 35. Guideposts 33 retain the carrierstrip 31 while the substrate 10 is being moved upwardly against thestop. It will be noted that the spacing from the wall 13 and the end ofthe lead portion 35 may be adjusted by the position of the stop 37. Asshown in Stage 5 of FIG. 4, the leads 35 are retained in place withinthe openings 15 of the substrate 10 by intimate contact with the innerwalls of the openings 15 because of the deformation 36 of the leads 35.The lead portions 35 are further securely retained in place by solderdeposition, wherein the substrate 10 and the lead frame may be passedthrough a solder bath. The solder layer 38 will cover each of theexternally extending portions of the leads 35 and the edge terminationareas 20 which, as previously stated, preferably extend slightlyinwardly of the openings 15. This arrangement provides a very secure andstable retention of the lead in the opening. That is, the lead extendssubstantially coextensive of the length of the opening to befrictionally gripped at its inwardly extending portion and additionallysecured by solder retention of the edge termination areas of thesubstrate 10. The stability of this means of retention will becomeimmediately apparent.

Stage 6 of FIG. 4 illustrates the substrate 10 with the carrier strip 31removed. The electrical circuitry, has not been shown in any of thestages of FIG. 4, but is deposited on the substrate prior to State 1 asdescribed in accordance with FIG. 3. The insulating conformal coating 40is, applied to the substrate following Stage 5 as indicated in Stage 6.The coating may be applied with well known dipping, brushing, sprayingor other techniques. The carrier strip 3 has also been cut and removedfrom the device as shown at Stage 6. The unit is then imprinted as shownin FIG. 7 with appropriate indicia 41.

Another embodiment of the present invention is disclosed in the assemblystages of FIG. 5. In this embodiment, there is contemplated the varioussteps of preparing a substrate as disclosed in FIGS. 1, 2, and 3, butwith an alternative form of through opening 45. With reference to Stage1 of FIG. 5, it will be observed that the openings 45 each include aninwardly extending abutment in the form of a counterbore defining ashoulder portion 46 for purposes hereinafter described. In this case,leads or the lead members 47 are preformed with a slightly enlargeddistal end portion 48. The enlarged portion 48 is limited in dimensionto allow free passage of the leads 47 in their respective openings 45 inthe substrate 10 (see Stage 2, FIG. 5). The distal end portions orextremities 48 of the lead portions 47 are then deformed by coining asindicated at Stage 3, or otherwise formed to insure that the extremities48 will not pass the shoulder portions 46 of the respective openings 45as the substrate is moved toward the stop 37. It will be apparent thatthe embodiment of FIG. 5 provides additional means for preventingwithdrawal of the leads 47 from the openings 45, should additional pullstrength be required. Stages 5 and 6 of FIG. 5 have been omitted,because they are the same as stages used in the embodiment of FIG. 4.

It will be understood that the electrical circuit components such as theresistive areas 23 may be printed on either or both of the top or bottomsurfaces 11 of the substrate 10, and that the lead portions 35 may be ofthe well known pin type (not shown). When the pin type lead portions areused, the insertion technique are those used with machines which handlewire leads. However, the pin type leads would be deformed in the samemanner as disclosed in the present invention to be compatable with thevarious stages of FIGS. 4 and 5.

We claim:
 1. A method of anchoring and connecting terminal leads to asubstrate containing electrical circuit components on a surface thereof,comprising the steps of:forming a substrate having a circuit supportingplanar surface, oppositely disposed planar sidewall surfaces dependingfrom and disposed angularly relative to said circuit supporting surface,and including a plurality of transversely disposed, spaced apartopenings extending through said substrate and intersecting each of thesidewall surfaces at opposite ends of each of said openings; depositinga conducting termination coating area disposed transversely of at leastone of said sidewall surfaces across one end of each of said openingsand overlapping a portion of said circuit supporting surface; depositinga layer of electrical circuit components on said circuit supportingsurface with connecting portions electrically connected to the saidtermination coating; providing a plurality of terminal leads; insertingindividual leads into their respective openings in said substrate with aportion of each lead extending outwardly from the opposite sidewall ofthe substrate; deforming the extending portion of said leads; and movingsaid substrate and said leads in a direction away from one another tocause the deformed portion of each of said leads to re-enter therespective opening and to be positioned for intimate contact with thesurface of said opening.
 2. The method of claim 1, wherein the formingstep provides a substrate with openings having substantially uniformcross-section throughout its length.
 3. The method of claim 2, whereinthe leads are formed from flat stock and are each deformed to provide atleast one corrugation across the flat surface, the depth of saidcorrugation being of greater lateral dimension than the dimension of thesurface of the respective opening in contact with the corrugation. 4.The method of claim 1, wherein the forming step provides a substratewith openings having a counterbore defining an inwardly extendingabutment intermediate the ends of the opening, and the respective leadsare deformed to engage the said abutment.
 5. The method of claim 4,wherein the leads are deformed by a coining operation to provide lateralprojecting portion of a dimension greater than the inwardly extendingabutment of said opening.
 6. The method of claim 1, wherein the terminalleads are provided as spaced apart, substantially parallel membersintegral with and laterally extending from an elongated carrier stripportion of a preformed lead frame assembly.